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no Drawin Original Ream! 11, 1e31 UNITED STATES PATENT OFFICE enema o. ctriannaQmw or wnrrs PLAINS, NEwYonx, ass'reuon. ro'caaianm m CARBON "CHEMICALS CORPORATION, A.

CORPORATION 01 NEW YORK 'rnnam nnoomrosrrronor mnocamions Nb. 1,648,849, dated October 18, 1927, Serial No. 78,898, aled January 7, 1826. Ap-

plication for reissue filed Kay 1, 1931. Serial Ho. B4388.

-- This invention comprises a process for ther: 1

mally decomposing hydrocarbons in gaseous or vapor form.

It is well known that hydrocarbons ingen- 7 described in Patent 1,460,545 granted on July 3, 1923, to Pierre E. Haynes and the present applicant, various materials have been investi ated to determine'their fitness for making tu esin which to confine hydrocarbons while heating them by products of combustion to temperatures as higli as 1000 C. Because of its fairly good strength and resistance to oxidation at the temperature involved,'but because of its cheapness, iron was the material first chosen for; the part of the,

principally tubes which-comes into contact with the combustion gases. 7 t

It was found, however, that ironexerts 'at' such temperatures a powerful catalytic action'on hydrocarbon vapors, promoting a reaction producing solid carbon, and the latter builds u'p on the walls of the tubes and soon clo them. It was therefore necessar to line the iron tubes with copper tubing. ince no iron or copper tubin obtainable at prices perinittingdts industria use for such a purpose has a snfliciently close approximationto a true c lindrical surface to permit the iron tube an its copper lining accurately to interfit, a gas layer 0 variable tllickness was pres ent between the two tubes and inter ered seriously with the heat transfer. Further". more the iron tubes burned out rather quickly and perforation of either the iron or thecopper disabled the unit. Replacement of tubes posed iron.-

.taining 26' to 29% chromium. The tubes are In an attempt to improve the lined tubes described above, chronte-iron was substituted for iron as the material of the jacket. This alloy was found to resist corrosion very much better than iron, but a more-important and entirely unexpected advantage of chromeiron was soon discovered. It was found that when the copper linin of a chrome-iron tube became perforated an the hydrocarbon gases came into contact with the acket, there was little or no deposition of carbon on the por,-'

tion of the jacket thus exposed, and no detrimental effect on the yield of olefine hydrocarbons. Under similar conditions. with iron jackets the tube would become blocked in a very short time by carbon built up onthe ex- Accordingly, it wasindicated that unlined chrome-iron'tubescould be substituted for copper-lined iron tubes with great advantage, and the unlined. tubes have gone into extensive'use andare giving excellent results.

For use at the temperatures discussed above, the chrome-iron preferably contains at least 20% of chromium, but the invention is not restricted to such percentages as a smaller proportion gives a useful effect, especially at lower operating temperatures.

" In speaking of such lower chromium content and/or lower temperatures, it is to be understood, however, that the range contemplated particularly concerns the treatment of hydrocarbons predominantly in gaseous phase, as distinguished from such operations as liquid phase oil cracking and-the like, where the occurrence of gaseous hydrocarbons is generally avoided insofar as possible. It is in the former cases, where the present -in vention is part'icularly efiective to prevent the commercially excessive carbon formation during decomposition which would'occur under similar operating conditions with commercial iron tubes. -The best results obtained so far have been with material conpreferably composed of a workable. alloy,

such'as is described in thepatent to Becket and McQu'igg, 1,454,464dated May 8, 1923. Seamless. draw tubing is preferred but tubes fabricated from sheet by fusionweld- 100 N ing may be used. The weld should be made with an alloy of approximately the same composition as the sheet forming the body of the tube. Even when this practice is followed a small amount of carbon may deposit on the weld when the tube is in use, presumably because the composition of the weld is somewhat-changed-in the'welding operation, ,as by oxidation of chromium. Carbon also accumulates slowly on the walls of any tube carrying heated hydrocarbon vapors in the temperature rangeabove mentioned presumably from the baking of heavy tars formed as by-products in the cracking reaction which condense out at the temperature of operation. This carbon is readily removed by periodically passing air through the tube while heating it to a suflicient temperature to bring aboutoxidation of the carbon. 1

lVhile the invention is especially valuable when used'in connection with the production of such olefines as ethylene and propylene by subjecting hydrocarbon materials to temperatures in the vicinity of 900 (1., it is applicable to many processes where'the temerature's and products are'quite different. he ability of chrome-iron to resist oxidation at high temperatures is, known, and the to said wall to heat t in the appended claims.

invention resides in the use of the alloy in contact with hydrocarbon material under such conditions that carbon deposition would preclude the use of commercial iron. It is intended to cover all such uses ofchrome-iron 1. The process which co prises thermally decomposing hydrocarbons particularly in gaseous or vapor form while the latter are in contact with an alloy consisting predominantly of chromium and iron under such conditions that contact of commercial iron with the decomposing hydrocarbon .would give rise, to ser ously interfering deposition of carbon. v

2. The process which comprises thermally decomposlng hydrocarbons while the latter are in contact with an alloy consistin predominantl of chromium and iron and containing at east 20% of chromium under such' said temperature by .contact of combustion gases therewith.

5. The process of making olefines which comprises subjecting hydrocarbons in gaseous form to thermal decomposition temperatures w hile pasing through a tube consisting predominantly ofchromium and iron and containing at least 20% of chromium under such conditions that contact of commercial iron with the decomposinghydrocarbons would give rise to seriously mterfering carbon formation and deposit.

6. The process of making olefines which comprises-subjecting hydrocarbons in gaseous form to temperatures causing rapid thermal decomposition thereof while passing through a tube consisting predominantly of chromium and iron and having a chromium content efl'ective to prevent theexcessive carbon formation and deposition which would occur with commercial iron under the same operating conditions. i

7. The process of making olefines without excessive carbon formation which comprises subjecting hydrocarbons in gaseous forms to rapid thermal decomposition at high temperatures while passing through a tube consisting' predominantly of chromium and iron and containing at least 20% of chromium. 8.- The process of making unsaturated hydrocarbons which com rises subjecting hydrocarbons in gaseous ihrm to temperatures causing rapid thermal decomposition thereof while passing through a tube consisting predominantly of chromium and iron and heating the exterior of said tube by contact of combustion gases therewith, said tube having a chromium content effective to prevent the excessive carbon formation during such decomposition and also effective to resist occur with commercial iron under the same operating conditions.

In testimony ture.

conditions that contact of commercial iron,

with the decomposing. hydrocarbon would give rise to seriously interfering deposition of carbon.

3. The process which comprises thermally decomposlng hydrocarbons by confining the I same at least in part by a wall constructed of chrome-iron containing at least 20% of chromium, and applyinlgcombustion gases e yd-rocarbons.

4. The process of thermally decomposing hydrocarbons which com rises confining the same in a chome-iron tu e resistant to oxidation at temperature as high as 900 0., and heating the exterior of the tube to about.

external scaling and corrosion which would GEORGE o. CURME,Jn.

whereof I aim: my signa- 

